1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image on a heat-sensitive recording material which is composed of a transparent carrier and a plurality of transparent heat-sensitive coupler layers deposited on the opposite surfaces of the transparent carrier. The transparent heat-sensitive coupler layers are each designed to produce a color having a different hue.
2. Description of the Related Art
Heat-sensitive recording systems are currently well known as one type of system for recording an image on recording paper by means of a heat-generating unit. Such a heat-sensitive recording system commonly employs a heat-sensitive recording material which is comprised by a carrier, such as ordinary paper or synthetic paper, coated with a coupler and a color developer. The heat-sensitive recording system is arranged to effect image recording by utilizing the process of heating the heat-sensitive recording material by means of a thermal head. This type of heat-sensitive recording method has the following advantages:
1. No development is needed.
2. The texture and quality of a carrier made of paper are close to those of ordinary paper.
3. The system is easy to handle.
4. Color density is high.
5. The recording apparatus is of a simple structure and is inexpensive.
6. The noise level of the system during recording operation is low compared to that of a dot printer or the like.
In recent years, heat-sensitive recording systems having the above-described advantages have rapidly been accepted in the field of monochromatic facsimile machines, printers and the like.
Moreover, in the field of information recording, the easy obtainment of a color hard copy from the terminal of information processing equipment such as a computer, a facsimile machine, or the like has been strongly desired. However, in order to obtain multi-color heat-sensitive recording materials, it is necessary that color forming mechanisms which are equivalent in number to the colors to be developed be provided on one carrier. The individual color-forming mechanisms must then be worked in a separately controlled manner. A large amount of effort has been directed toward the realization of such a multi-color heat-sensitive recording system, but no system has been proposed which achieves the adequate representation of the color hues and the satisfactory separation of colors.
As described above, an opaque carrier such as ordinary paper or synthetic paper is commonly applied to the carrier of the heat-sensitive recording material. This is simply because a color image is usually read in the form of an image reflected from one surface of the recording material.
Examples using transparent matter as carriers of heat-sensitive recording materials are disclosed in Japanese Patent Publication No. 20151/1965, Japanese Patent Application Nos. 68875/1985 and 184483/1985. The object common to these prior inventions is to enable a high-contrast image or a high-quality image of superior gloss to be obtained when a thermally recorded image is viewed from the direction of the transparent carrier. Moreover, another invention is proposed in which heat-sensitive recording layers each having a different color hue are deposited on the opposite surfaces of a transparent carrier, in order to obtain a color image of two or more colors (refer to Japanese Patent Laid-open Nos. 114431/1974, 3640/1975 and 4092/1975).
In accordance with these proposals, however, coupler components and color development components are merely dispersed in a solid state in the heat-sensitive coupler layers. The coupler layers therefore become substantially opaque due to the scattering of light. Accordingly, it is impossible to obtain the desired multi-color image composed of clearly separated colors. In accordance with the invention disclosed in Japanese Patent Laid-open No. 4092/1975, it is suggested that individual components be molten and applied as one layer in order to improve the transparency of a heat-sensitive coupler layer. In this case, however, since each component tends to easily produce its color prior to printing, a so-called fog may appear. For this reason, the possible number of steps of color separation is limited and, therefore, this multi-color recording material is still substantially insufficient.
To overcome the above-described problems, the applicant proposed a multi-color heat-sensitive recording material composed of a transparent carrier and coupler layers formed on the opposite surfaces of the transparent carrier. The coupler layers were substantially transparent and capable of producing colors each having a different hue. With this multi-color heat-sensitive recording material, it is possible to provide a thermal color image whose quality improves on those of conventional thermal color images (Japanese Patent Application Nos. 80787/1076, 88196/1977, and 75409/1977).
With this multi-color heat-sensitive recording material, it is possible to obtain a multi-color image having excellent hues superior color separation characteristics and improved storage life. Heretofore, these 3 aspects have never been achieved by a heat-sensitive recording system. In addition, it is possible to convert the obtained image into a transmitted image or a reflected image.
Since this type of heat-sensitive recording paper has opposite surfaces coated with coupler layers, it is necessary to heat both surfaces by means of one or more thermal heads. In the case of heat-sensitive recording paper having opposite surfaces either of which is coated with multiple coupler layers, it is necessary that the uppermost layer (the layer nearest to the surface) be colored by the application of heat having an intensity such that the other layers are not heated. After the colored layer has been fixed, the other layers need to be heat treated.
The basic procedure for recording an image on heat-sensitive recording paper will be explained below with reference to FIGS. 11(A) to 11(E). As shown in FIG. 11, a heat-sensitive recording material 10 includes a carrier which is a polyester film (hereafter referred to as "PET") 125, on which a magenta dye layer (hereinafter referred to as "M-dye layer") 126 is formed on one surface. On the M-dye layer 126, a yellow dye layer (hereinafter referred to as the "Y-dye layer") 128 is formed. On the other surface of the carrier is formed a cyan dye layer (hereinafter referred to as the "C-dye layer") 130. This heat-sensitive recording material 10 is transparent at room temperature. The Y-dye layer 128 is of the light fixing type which does not undergo any variation during heating after it has been irrdiated with light rays of wavelength 400 nm from a light source 131. A recording head 133 is disposed on the upper side of the heat-sensitive recording material 10 as viewed in, for example, FIG. 11(A).
Referring to FIG. 11(A), the Y-dye layer 128 is heat treated by means of a recording head 133. In this heating step, the intensity of heat is selected so as not to develop the color of the M-dye layer 126 underlying the Y-dye layer 128. Accordingly, the color of the Y-dye layer 128 alone is developed.
Referring next to FIG. 11(B), the Y-dye layer 128 is irradiated with light rays with a wavelength of approximately 400 nm, thereby fixing the Y-dye layer 128 so that the color thereof does not undergo any variation during subsequent heating.
Referring to FIG. 11(C), the M-dye layer 126 is heated at an intensity which is greater than that of the heat applied to the Y-dye layer 128. Thus, the color of the M-dye layer 126 is developed.
Referring next to FIG. 11(D), the heat-sensitive recording material 10 is turned upside down and, as shown in FIG. 11(E), the C-dye layer 130 is heated.
If another recording head 135 is disposed on the underside of the heat-sensitive recording material 10 (as shown by phantom lines in FIG. 11(A)), the C-dye layer 130 is heated without turning the recording material 10 upside down. In this case, the color of the C-dye layer 130 is developed by applying heat thereto at such an intensity that it does not affect the M-dye layer 126 formed on the side of the PET 125 opposite the C-dye layer 130.
However, no image recording apparatus capable of automatically effecting this image recording procedure has currently been developed. In order to realize an image recording apparatus for recording an image on a multi-color heat-sensitive recording material, the following requirement must be satisfied: the heat-sensitive recording material must be able to be accurately positioned so that one image can be recorded in steps the number of which is the same as the number of color layers to reproduce the color of the image. However, as long as this positioning step is not automated, it is difficult to ensure high-speed processing which is comparable to the processing speeds of conventional apparatus.